1. Field of the Invention
The present invention relates to a fuel pressure controller applied to a fuel supply system having a fuel pump that has an electromagnetic discharge metering valve for regulating a fuel amount discharged to an outside out of suctioned fuel and that is driven by a driving force of an internal combustion engine and a pressure accumulation chamber that accumulates the fuel pressure-fed by the fuel pump at a high-pressure state, the fuel pressure controller controlling fuel pressure in the pressure accumulation chamber by operating the discharge metering valve.
2. Description of Related Art
JP-A-H4-272471 describes a fuel supply system of this kind structured such that fuel is suctioned when a plunger of a fuel pump moves to a bottom dead center and such that a discharge metering valve is closed through electromagnetic drive to break communication between a fuel supply side and a plunger side when the plunger moves to a top dead center. This fuel supply system discharges the fuel remaining on the plunger side from the fuel pump to an outside when the metering valve is closed. JP-A-H4-272471 describes a fuel pressure controller that calculates a basic value of valve closing timing of the metering valve based on a target value of the fuel pressure in a pressure accumulation chamber (common rail) common to respective cylinders and a command value of an injection amount of an injector and that performs feedback correction of the basic value based on a difference between a sensed value of the fuel pressure and the target value of the fuel pressure. Thus, the fuel amount can be suitably regulated.
A force applied to the metering valve by the fuel increases if rotation speed increases. In such a case, there is a possibility that the metering valve closes (i.e., causes spontaneous closure) and the fuel is discharged from the fuel pump unintentionally although the closing operation of the metering valve is not performed. Therefore, the above-described fuel pressure controller operates the metering valve to a closed state constantly under such the situation. Thus, the fuel pressure controller stops the suctioning of the fuel when the plunger moves to the bottom dead center to prohibit the discharge of the fuel from the fuel pump.
Inventors of the present invention found that the minimum value of the rotation speed causing the spontaneous closure of the metering valve is lower than a value at which the force applied by the fuel is balanced out with a force of a member for opening the metering valve. This is attributed to the fact that the closing of the metering valve is facilitated by a residual magnetic flux remaining after the closing operation of the metering valve. Therefore, stoppage of the fuel pressure-feeding operation of the fuel pump is required at rotation speed lower than the maximum rotation speed, which is decided by mechanical properties and is not supposed to cause the closure of the metering valve.
A circuit for removing the residual magnetic flux of the metering valve may be provided. However, this can cause an increase in the size of a drive circuit driving the metering valve or an increase in the number of components.